1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief Cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.77 and 4.6 GeV
 10  class BESIII_2016_I1495838 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1495838);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      declare(FinalState(), "FS");
 23      declare(UnstableParticles(), "UFS");
 24      book(_nPsi, "TMP/psi");
 25    }
 26
 27    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 28      for (const Particle &child : p.children()) {
 29        if(child.children().empty()) {
 30          --nRes[child.pid()];
 31          --ncount;
 32        }
 33        else
 34          findChildren(child,nRes,ncount);
 35      }
 36    }
 37
 38    /// Perform the per-event analysis
 39    void analyze(const Event& event) {
 40      const FinalState& fs = apply<FinalState>(event, "FS");
 41      map<long,int> nCount;
 42      int ntotal(0);
 43      for (const Particle& p: fs.particles()) {
 44        nCount[p.pid()] += 1;
 45        ++ntotal;
 46      }
 47      const FinalState& ufs = apply<FinalState>(event, "UFS");
 48      // find the psis
 49      for (const Particle& p :  ufs.particles(Cuts::pid==443)) {
 50        if(p.children().empty()) continue;
 51        map<long,int> nRes = nCount;
 52        int ncount = ntotal;
 53        findChildren(p,nRes,ncount);
 54        // psi pi+pi-
 55        if(ncount!=2) continue;
 56        bool matched = true;
 57        for(auto const & val : nRes) {
 58          if(abs(val.first)==211) {
 59            if(val.second !=1) {
 60              matched = false;
 61              break;
 62            }
 63          }
 64          else if(val.second!=0) {
 65            matched = false;
 66            break;
 67          }
 68        }
 69        if(matched) {
 70          _nPsi->fill();
 71          break;
 72        }
 73      }
 74    }
 75
 76    /// Normalise histograms etc., after the run
 77    void finalize() {
 78      double fact =  crossSection()/ sumOfWeights() /picobarn;
 79      double sigma = _nPsi->val()*fact;
 80      double error = _nPsi->err()*fact;
 81      for(unsigned int ix=1;ix<3;++ix) {
 82        Estimate1DPtr  mult;
 83        book(mult, ix, 1, 1);
 84        for (auto& b : mult->bins()) {
 85          if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 86            b.set(sigma, error);
 87          }
 88        }
 89      }
 90    }
 91
 92    /// @}
 93
 94
 95    /// @name Histograms
 96    /// @{
 97    CounterPtr _nPsi;
 98    /// @}
 99
100
101  };
102
103
104
105  RIVET_DECLARE_PLUGIN(BESIII_2016_I1495838);
106
107}